Welding devices for joining a pair of workpieces by a weldment which bridges across a gap between the workpieces are well known. For the most part they have been employed for the butt welding of two metal plates whose juxtaposed edges are spaced apart to form a welding gap between them. To prevent the pool of weld metal from flowing downwardly through the gap and thus out of the desired location between the edges, it has been proposed heretofore to provide a bath support below the welding gap. This support for the pool of weld metal confines the molten material between the flanks or edges of the workpieces and supports the base of the weld seam until the weld metal solidifies.
In one prior-art concept, the pool support is constituted by a band or strip of material which extends along the entire length of the weld seam. This band is pressed against the underside of the bead of weld material, e.g. by being pressed against the undersides of the two spacedly juxtaposed workpiece plates.
When however, the bead is to be formed between edges of a pair of parallel plates which are disposed in spaced apart vertical planes, the underside of the bead is no longer accessible and it is impossible to press a band or strip of a pool-support material against the underside of the bead.
In these cases it is not uncommon to fit a structure between the plates to define the bottom of the pool of weldment and hence the bottom of the hardened bead. This material should be frangible so that it can be broken up into small pieces by impact or the like to enable its removal from the narrow gap between the workpiece plates. Welding systems of this type are relatively expensive and it is frequently not possible to remove all of the pool-support material. The use of this technique, moreover, is not possible where a pair of coextensive plates are to be welded peripherally together in spaced-apart relationship to define, for example, a compartment between them, e.g. for use in heat exchangers. In this case, at least the support for the last weld bead cannot be removed, or can be removed only with the greatest difficulty.